The purpose of this randomized controlled trial is to investigate the non-inferiority, and possible superiority, of a high-dose home-based tDCS protocol compared with a conventional home-based protocol, and to assess its cost-effectiveness, in patients with major depression.

As a secondary aim, we aim to assess the predictive value of baseline EEG for clinical response to high-dose home-based tDCS treatment in patients with major depression.

Inclusion Criteria:

• Patients aged 18 years or over.
• Patients diagnosed with Major Depressive Disorder with a current depressive episode, based on the criteria of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) (American Psychiatric Association, 2013).
• Score on the Hamilton Depression Rating Scale (HDRS-17) ≥16 (Hamilton et al., 1960).
• Patients on a stable prescription of antidepressants/pharmacological medication and who agree to continue this throughout the study; and/or, if undergoing psychotherapy, who have maintained this treatment consistently for at least 6 weeks.
• Demonstrate the ability to apply home-based tDCS appropriately, either independently or with the help of a carer.
• Have access to an electronic device with a camera to enable monitoring of the intervention, as well as to contact the participant.
• Have the ability and willingness to commit to the study team to complete all phases of the study.
• Volunteer to participate and sign the specific informed consent form for this study.

Exclusion Criteria:

• Patients with a current manic episode as determined by the Young Mania Rating Scale (YMRS), or a psychotic episode as defined by the MINI scale.
• Patients who answer 'yes' to questions 4, 5 or 6 of the Columbia Suicide Severity Rating Scale (C-SSRS), a risk assessment and identification tool.
• Patients with treatment-resistant depression, defined as an inadequate clinical response to two or more courses of antidepressant treatment at appropriate doses and duration.
• Any previous hospitalisation for suicidal behaviour.
• Presenting with current chronic or severe insomnia (< 4 hours' sleep per night) or sleep apnoea.
• Presence of any structural lesion (e.g., any structural neurological condition or more subcortical lesions than would be expected for their age, or having suffered a stroke affecting the stimulated area or connected areas) or any other clinically significant abnormality that may affect safety, participation in the study, or confound the interpretation of study results, as determined by the investigator.
• History or presence of any other condition or comorbidity associated with TDM: cardiac or neurological conditions, cognitive impairment.
• History of or current diagnosis of any other mental disorder: obsessive-compulsive disorder, bipolar disorder (type 1 or 2), anxiety disorder, agoraphobia, eating disorders, personality disorders.
• Any exclusion criteria other than those established by clinical guidelines on non-invasive brain stimulation (Woods et al., 2016):
• Metal implants or head injuries, any electronic devices such as cochlear implants or cardiac pacemakers
• Brain stimulation within the last 6 months.
• Clinical or family history of epilepsy or seizure episodes.
• Presence of dermatological problems (allergic skin reaction at the electrode site, psoriasis, etc.)
• History of drug or alcohol abuse during the study or in the 3 months prior (with the exception of nicotine).
• Pending trial or litigation during the course of the trial.
• Pregnancy.

In accordance with the recommendations of the International Committee of Medical Journal Editors, the de-identified individual participant data (IPD) that underlie the results reported in this study will be shared. The data will become accessible one year after the publication of the primary results and will remain available for five years. Access will be provided to researchers who inquire and agree to a data-use agreement through Ionclinics (investigacion@ionclinics.com/ensayos@ionclinics.com). The data will be de-identified and shared in accordance with applicable regulations and the informed consent provided by the participants.

EEG analyst will be blinded from group treatment.